JPS6042533Y2 - FM receiver - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an FM receiving device for receiving FM broadcast radio waves and listening to FM broadcasts.

In this type of FM receiver, the frequency -
Performing voltage conversion.

Therefore, during tuning and detuning, a DC potential is generated at the output of the FM detection stage, and this appears as shock noise.

Therefore, multi-stage DC blocking coupling capacitors are inserted into audio signal circuits such as the stereo demodulator, which is the next stage after the FM detection stage, and even the output amplifier. It was not possible to completely eliminate shock noise, and there were problems such as deterioration of sound quality and reliability due to the insertion of multiple stages of coupling capacitors.

Furthermore, a direct current potential may be generated in the audio signal circuit, and in addition, conventionally, the multi-stage coupling capacitors described above have been required.

This invention was made in view of the above points, and the object is to provide an FM receiving device that can completely eliminate shock noise and can also eliminate multi-stage coupling capacitors.

An embodiment of this invention will be described below with reference to the drawings.

Figure 1 is a circuit configuration diagram of an FM receiver. In this figure, 1 is an antenna that receives FM broadcast waves, and the FM broadcast waves (FM broadcast signals) received by this antenna 1 are amplified by a high frequency amplifier 2. After that, the signal is supplied to the first mixer 4 together with the output signal of the first local oscillator 3 and converted into a signal of the first intermediate frequency.

Further, this first intermediate frequency signal is amplified by the first intermediate frequency amplifier 5, and then supplied to the second mixer 7 together with the output signal of the second local oscillator 6, where it is converted into a second intermediate frequency signal. .

Thereafter, this second intermediate frequency signal is supplied to the 1M detector 8 and subjected to FM detection.Furthermore, this FM detection output is supplied to the stereo demodulator 9 and separated into left and right signals. The output signals are sent to output amplifiers 10□, 102
The signal is amplified at 111.11° and output to the output terminal 111.11°.

The above has been a description of the main components of the FM receiver, which has a double-convert superhetero gain configuration, but this FM receiver is further configured as follows.

That is, the configuration is such that only a DC component is extracted from the output of the 1M detector 8 using a resistor 12 and a capacitor 13, and this DC component is fed back to the second local oscillator 6. The oscillation frequency is controlled by the DC component.

That is, in such a configuration, when a DC potential is generated at the output of the 1M detector 8 during tuning or detuning, this DC potential is fed back to the second local oscillator 6.

Then, the oscillation frequency of the second local oscillator 6 is controlled so that the DC potential at the output of the FM detector 8 that performs frequency-voltage conversion becomes zero, and such feedback control is instantaneous. As a result, generation of a DC potential at the output of the FM detector 8 during tuning and detuning is prevented.

However, if such feedback control is performed in a single-convert superhetero gain configuration, the problem arises that even if you try to detune the station, it will keep pulling the station.

However, the above 9M receiver has a double-convert superhetero gain configuration, so even if such feedback control is performed, the above-mentioned problem does not occur.

In addition, recently, so-called synthesizer tuners have appeared, and since this also has a double-conversion configuration, the feedback control described above can be implemented in the same way.

Further, when the above-described feedback control is performed, the frequency characteristics of the signal system may deteriorate due to the resistor 12 and capacitor 13 for this purpose.

Therefore, when it is desired to sufficiently improve the frequency characteristics, as in the other embodiment shown in FIG. When the variable resistor 12'
is set to a sufficiently small value so that frequencies below the low frequency are sufficiently fed back as DC components, and the tuning knob 14 is
When the hand is removed, the value of the variable resistor 12' becomes larger, so that only the very low frequency is fed back as a DC component.

It goes without saying that the same effect can be obtained by changing the capacitance of the capacitor 13 instead of the value of the resistor.

In addition, in the case of a synthesizer tuner, variable resistor 1
2' or the capacitance switching signal of the capacitor 13 may be obtained from the channel selection switch.

In addition, the above explanation is about preventing the generation of DC potential at the FM detector 8 output during tuning and detuning, but the 1M
A DC potential may be generated at the stereo demodulator 9, which is the next stage of the detector 8, and also at the output amplifier 10□, 10°.

In such a case, as shown by the broken line in FIG. 1, a resistor 12. is connected to the output of the stereo demodulator 9 or the output of the output amplifier 101. ．． 12□ to output the stereo demodulator 9 or the output amplifier 10. ．． If the DC component is fed back from the output of 10□, the generation of DC potential from them can be eliminated in the same way.

In addition, when feeding back the DC component after separating such a signal into left and right signals, as shown in Figure 1, the sum of the left and right DC components may be fed back, or only one side of the left or right side may be fed back. The DC component may also be fed back.

Therefore, according to such an FM receiving device, tuning,
It is possible to prevent the generation of DC potential at the output of the FM detector 8 during detuning, completely eliminating shock noise, and also to prevent the generation of DC potential in audio signal circuits such as the stereo demodulator 9 and the output amplifiers 10□, 10°. It is possible to eliminate multi-stage coupling capacitors from this audio signal circuit, and by eliminating these coupling capacitors, it is possible to improve the sound quality and reliability. It can be simplified and has great effects as described above.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing one embodiment of an FM receiver according to this invention, and FIG. 2 is a circuit diagram showing another embodiment of this invention. 1...Antenna, 3...First local oscillator 4...First mixer, 6...Second local oscillator, 7...・Second mixer, death...-F
M detector, 9... Stereo demodulator, 101, 1
0゜・・・Output amplifier, 12・・・Resistor,
13... Capacitor.

Claims (1)

[Scope of utility model registration request] Double convert superhetero gain configuration and waist FM
It is characterized by comprising means for extracting only the DC component from the signal system after the detection stage, and means for feeding back this DC component to a second local oscillator to control the oscillation frequency so that the DC component becomes zero. FM receiver.